In a paper entitled "Magnetoacoustic Excitation of Radio-Frequency Resonances and Echoes in Magnetic Materials" by M. Rubinstein et al which appeared in the January 1968 Journal of Applied Physics, Vol. 19, Number 1, pp. 81-88, powdered magnetoacoustic garnets and ferrites were used to produce echo pulses after an r. f. excitation of the powder. However, their circuit for producing echo pulses did not involve storage of information. In a sample of magnetoacoustic powder such as lithium ferrite, Rubinstein et al excited the powder at time t=0 with an intense, short r. f. pulse and, at a time t=.tau. later, a second short intense pulse of the same frequency was applied to the powder. As a consequence of said second applied pulse, an echo pulse, having the same fundamental frequency as the excitation pulse, was produced at a time after the second pulse equal to the time interval between the two exciting pulses. The echo pulse had a decay time of T.sub.2. When a third pulse of the same frequency as the first two pulses was applied to the powder at time T after the first echo a second echo appeared. However, the decay time T.sub.1 of the second echo pulse obeyed the relation T.sub.1 = T.sub.2 /2. Since T.sub.2 is very short, less than one millisecond, the third pulse, which served as a reading pulse, had to be applied at a time T that was of the order of one millisecond. It is obvious that such a device cannot be used as a useful memory or storer of information.
The present invention employs powdered magnetoelastic materials, like Rubinstein et al, but by choosing appropriate minimum energy levels for our exciting pulses and selecting specific magnetoelastic powders, information storage, as long as several minutes and greater, can be achieved.
Consequently it is an object of this invention to employ magnetoelastic powders in a resonant circuit so as to achieve useful storage times of information applied as an r. f. signal to said powders.